DE 198 08 590 A1 discloses a respiratory humidifier which comprises a hose pump as dosing means and an electrically heated evaporator. The hose pump transports water from a commercially available water bag in the required amount so as to obtain a predetermined relative breathing gas humidity at a predetermined breathing gas temperature. The evaporator makes water at a temperature above 134° C. available, which heats the breathing gas to the predetermined breathing gas temperature when being mixed with the breathing gas to be humidified. Preferably, a thermal insulation is provided between the outlet side of the evaporator and a breathing gas channel in order to avoid, if possible, a heating of the breathing gas channel by the respiratory humidifier also without the supply and evaporation of water. The outlet opening of the evaporator preferably projects into the breathing gas channel. The high heating temperature results from the desire to destroy germs which may exist in the water, since the hygiene provisions for vapor sterilization say that a sufficient germ reduction is achieved if the germs are exposed to a temperature of 134° C. for three minutes.
Respirators also include the so-called CPAP-apparatus which serve the treatment of apneas during the sleep. To this end, the CPAP (continuous positive airway pressure) therapy was developed, which is described in Chest. Volume No. 110, pages 1077–1088, October 1996 and in Sleep, Volume No. 19, pages 184–188. A CPAP-apparatus generates a positive overpressure up to approximately 30 mbar by means of a compressor or turbine and administers the same, preferably via a humidifier, via a hose and via a nose mask, to the respiratory tract of the patient. This overpressure is to ensure that the upper respiratory tract remains fully opened during the whole night, so that no apneas will occur (DE 198 49 571 A1). A humidifier used in conjunction with said CPAP-apparatus prevents the patient's mucous membranes from desiccating.
A breathing gas humidifier for CPAP-apparatus is described in DE 199 36 499 A1. The humidifier comprises a refill unit formed of a tub element and a pot part coupled therewith, which can be removed from a mountable casing. The tub element and the pot part are imperviously connected with each other. In conjunction with a partition wall a storage room for a liquid is formed in said pot part, which contains the major part of the water reserve provided for humidifying the breathing gas. A separate humidifying zone is formed in the tub element disposed underneath the pot part, which merely contains a small portion of the water reserve. The height of the water in the tub element is kept at a predetermined level by a dosing device. In the course of the gradual evaporation of the water located in the tub element water from the liquid storage room is successively or continuously refilled. Via a breathing gas inlet opening the breathing gas is blown through the upper portion of the tub element to a breathing gas outlet opening. The bottom area of the tub element is heated by a heating device. For increasing the thermal transmission, the bottom area of the tub element is made of a material having a high thermal conductivity, e.g. metal.
DE 299 09 611 U1 and DE 200 10 553 U1 likewise describe humidifiers for respirators in which the air is passed over the surface of a heatable water reservoir.
DE 298 19 950 U1 describes in connection with a heatable respiratory humidifier a phase control mechanism and a control circuit for controlling the power supplied to a heating element. The heating element heats a water bath. The control can either be accomplished such that the heating element is supplied with a constant power or that the water bath is kept at a constant temperature.
Documents G-94 09 231.1 and DE 298 17 685 U1 deal with lids for storage vessels for the water reserve of humidifiers for CPAP-apparatus. During operation the lids seal the storage tank in a pressure-proof manner allowing breathing air to be blown through the upper portion of the storage vessel not filled with water, whereby the lid can slightly be opened for refilling water.
It is desirable to provide a simple evaporator for respirators and a simple method, with the evaporator and the method consuming a small amount of energy.